A solution contains naphthalene (C10H8) dissolved in hexane (C6H14) at a concentration of 15.00% naphthalene by mass. Calculate the vapor pressure at 25 ∘C of hexane above the solution. The vapor pressure of pure hexane at 25 ∘C is 151 torr. I keep getting 168 torr but it says I am wrong please help me understand what I am doing wrong.
To calculate the vapor pressure of hexane above the solution, you need to apply Raoult's law, which states that the vapor pressure of a component in an ideal solution is directly proportional to its mole fraction in the solution.
First, let's find the mole fraction of hexane in the solution:
1. Calculate the mole fraction of naphthalene (C10H8):
- Determine the molar mass of C10H8:
M(C10H8) = 10*(12.01 g/mol) + 8*(1.01 g/mol) = 128.18 g/mol
- Calculate the moles of naphthalene:
Moles of C10H8 = (15.00 g C10H8) / (128.18 g/mol) = 0.1170 mol C10H8
2. Calculate the mass of hexane (C6H14) in the solution:
- Mass of hexane = 100 g - 15.00 g = 85.00 g
3. Calculate the moles of hexane (C6H14):
Moles of C6H14 = (85.00 g C6H14) / (86.18 g/mol) = 0.9854 mol C6H14
4. Calculate the mole fraction of hexane:
Mole fraction of C6H14 = Moles of C6H14 / (Moles of C10H8 + Moles of C6H14)
= 0.9854 / (0.9854 + 0.1170)
≈ 0.894
Now that we have the mole fraction of hexane, we can calculate the vapor pressure of hexane above the solution using Raoult's law:
Vapor pressure of hexane above the solution = Mole fraction of hexane * Vapor pressure of pure hexane
Vapor pressure of hexane above the solution = 0.894 * 151 torr
= 134.94 torr
Therefore, the vapor pressure of hexane above the solution at 25 °C is approximately 134.94 torr.
Nevermind i got the answer(:
It is 135 Torr